The present invention relates in general to photolithography used in the manufacture of semiconductor devices, and particularly to a reticle stage and method of increasing throughput.
In the manufacture of semiconductor or electronic devices, photolithographic techniques or processes are often used. In the photolithographic or lithographic process, a circuit pattern contained on a mask or a reticle is projected or imaged onto a photosensitive substrate. The now patterned after processing photosensitive substrate is further processed to form a semiconductor or other electronic device by well known techniques. The substrate is typically a wafer. As the feature sizes required to be printed become smaller, different techniques for imaging the features become necessary. One technique for providing an improved quality of printing of the pattern is the use of a phase shift mask or reticle. The use of a phase shift mask or reticle generally requires the exposure of the same field or area on a photosensitive substrate or wafer first with a phase shift mask and second with a trim mask. The trim mask is physically distinct from the phase shift mask and may be printed with separate exposure conditions. Accordingly, where the photolitographic process requires exposure of the same field on a photosensitive substrate with different masks, the masks must be changed between each exposure. This change greatly reduces throughput and often creates potential alignment problems. A time consuming and potentially error prone alignment process must be done for each mask used to expose the field on the photosensitive substrate or wafer. Accordingly, there is a need for a reticle stage and method for exposing the same field with at least two different masks or reticles in a manner to increase throughput and prevent alignment or calibration problems. There will always be a decrease in throughput as the wafer is essentially exposed twice. There is a need to eliminate this loss in throughput to close to the unavoidable two exposure loss.
The present invention is directed to a reticle stage and method for increasing throughput, and improving alignment when multiple masks or reticles are used during a double exposure of a field on a photosensitive substrate. A reticle stage is used in a scanning photolithographic tool or device comprising at least two masks or reticles. This invention can also be applied to a step and repeat system. The reticle stage has a range of motion permitting at least two masks or reticles to be scanned sequentially exposing the same field to two different patterns on a photosensitive substrate. In another embodiment, the reticle stage may have a third calibration reticle placed adjacent to one of at least two masks or reticles. At least one photosensitive substrate or wafer plane detector is used in combination with the calibration reticle or mask providing real time system calibration. The present invention is particularly suited for use with phase shift masks or reticles and associated trim masks or reticles.
Accordingly, it is an object of the present invention to provide increased throughput when the system is used in a double exposure mode.
It is another object of the present invention to improve alignment between exposures of the same field with at least two masks or reticles.
It is an advantage of the present invention that manufacturing costs are reduced.
It is a further advantage of the present invention that the same field can be exposed with at least two masks or reticles without requiring a mask or reticle change and realignment.
It is a feature of the present invention that a mask or reticle stage is used with at least two reticles or masks that has a range of motion permitting scanning of the at least two masks or reticles.
It is another feature of the present invention that a calibration reticle or mask is used in combination with at least one substrate or wafer plane detector.
These and other objects, advantages, and features will become readily apparent in view of the following more detailed description.